Take a crack at killing security warnings. Fail miserably. Keep the new code because it's a bit nicer.

--HG--
branch : xslt

common/content/util.js

@@ -365,6 +365,48 @@ const util = { //{{{
         }
     },
 
+    /**
+     * Evaluates an XPath expression in the current or provided
+     * document. It provides the xhtml, xhtml2 and liberator XML
+     * namespaces. The result may be used as an iterator.
+     *
+     * @param {string} expression The XPath expression to evaluate.
+     * @param {Document} doc The document to evaluate the expression in.
+     * @default The current document.
+     * @param {Node} elem The context element.
+     * @default <b>doc</b>
+     * @param {boolean} asIterator Whether to return the results as an
+     *     XPath iterator.
+     */
+    evaluateXPath: function (expression, doc, elem, asIterator)
+    {
+        if (!doc)
+            doc = window.content.document;
+        if (!elem)
+            elem = doc;
+        if (util.isArray(expression))
+            expression = util.makeXPath(expression);
+
+        let result = doc.evaluate(expression, elem,
+            function lookupNamespaceURI(prefix)
+            {
+                return {
+                    xhtml: "http://www.w3.org/1999/xhtml",
+                    xhtml2: "http://www.w3.org/2002/06/xhtml2",
+                    liberator: NS.uri
+                }[prefix] || null;
+            },
+            asIterator ? XPathResult.ORDERED_NODE_ITERATOR_TYPE : XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,
+            null
+        );
+
+        result.__iterator__ = asIterator
+                            ? function () { let elem; while ((elem = this.iterateNext())) yield elem; }
+                            : function () { for (let i = 0; i < this.snapshotLength; i++) yield this.snapshotItem(i); };
+
+        return result;
+    },
+
     /**
      * The identity function.
      *